Innovations in diagnosing and verifying the level of success of treatment of disease have progressed from solely external imaging processes to include internal diagnostic processes. In addition to traditional external image techniques such as X-ray, MRI, CT scans, fluoroscopy, and angiography, small sensors may now be placed directly in the body. For example, diagnostic equipment and processes have been developed for diagnosing vasculature blockages and other vasculature disease by means of ultra-miniature sensors placed upon the distal end of a flexible elongate member such as a catheter, or a guide wire used for catheterization procedures. For example, known medical sensing techniques include intravascular ultrasound (IVUS), forward looking IVUS (FL-IVUS), fractional flow reserve (FFR) determination, a coronary flow reserve (CFR) determination, optical coherence tomography (OCT), trans-esophageal echocardiography, and image-guided therapy.
One exemplary type of procedure involves pressure measurements within a blood vessel. A currently accepted technique for assessing the severity of a stenosis in the blood vessel, including ischemia causing lesions, is fractional flow reserve (FFR). FFR is a calculation of the ratio of a distal pressure measurement (taken on the distal side of the stenosis) relative to a proximal pressure measurement (taken on the proximal side of the stenosis). FFR provides an index of stenosis severity that allows determination as to whether the blockage limits blood flow within the vessel to an extent that treatment is required. The normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and require treatment. Another technique for assessing blood vessels utilizes Instant Wave-Free Ratio™ Functionality (iFR® Functionality) (both trademarks of Volcano Corp.), which includes the determination of a pressure ratio across a stenosis during the wave-free period, when resistance is naturally constant and minimized in the cardiac cycle. The iFR modality does not require administration of a hyperemic agent. The normal value of iFR in a healthy vessel is 1.00, while values less than about 0.89 are generally deemed significant and require treatment.
When an occluded blood vessel that requires treatment is identified, a percutaneous coronary intervention (PCI) is a therapeutic procedure that can be utilized to treat the vessel. A PCI includes angioplasty and positioning a stent across the stenosis to open the vessel. Clinicians conventionally rely on angiography and physiologic measurements of pressure and/or flow, which are not meaningfully connected, to plan a therapeutic intervention. Planning the therapeutic intervention can include selecting various parameters related to the stent, such as positioning, length, diameter, etc. Because it is difficult to integrate the various sources of data, there is difficulty in developing the therapeutic plan. Further, there is little ability to predict the efficacy of the therapeutic intervention based on the available data. For example, a clinician conventionally cannot determine, with a clinical certainty that is supported by the collected data, what the effect of changing the positioning and/or length of a stent is on the efficacy of the stent placement.
Accordingly, there remains a need for improved devices, systems, and methods for assessing the severity of a blockage in a vessel and, in particular, a stenosis in a blood vessel. There also remains a need for improved devices, systems, and methods for planning a PCI by connecting the angiography and physiologic data in a way that allows clinicians to efficiently plan and evaluate the proposed therapy. Further, there remains a need for providing visual depictions of a vessel and a proposed therapeutic intervention, such as a stent, in the vessel that allow a clinician to plan, evaluate, and change the proposed therapy in a manner supported by the collected physiologic data.